6sl7 front end

[passfan]

I'm going to experiment with a couple of 6sl7 tubes I've got lying around just to try something different. It will be something more Rocket like in simplicity and maybe later , if this turns out okay an Express style. If anyone has any suggestions they are more than welcome to offer them.

[funkmeblue]

I've built a 6sl7 express a couple of years ago and it's one of my favorites. Great cleans and really sings when cranked, really likes kt66's.

[passfan]

I've built a 6sl7 express a couple of years ago and it's one of my favorites. Great cleans and really sings when cranked, really likes kt66's.

Did you run loadlines and redesign or do anything special , or just drop in replacements ? I'm going to combine these with a big bottle power section in the rocket (6L6GC's).

[funkmeblue]

I used Aiken's phase inverter http://www.aikenamps.com/ , I changed the 150k dropping resistor before the 3rd gain stage to 220k and added a cut control. The cut control allows me to crank the presence for more juicy gain, back off the cut to keeps the highs in check. I also paralleled the 3rd gain stage with a 50k plate and a 5k cathode resistor.

[passfan]

I used Aiken's phase inverter http://www.aikenamps.com/ , I changed the 150k dropping resistor before the 3rd gain stage to 220k and added a cut control. The cut control allows me to crank the presence for more juicy gain, back off the cut to keeps the highs in check. I also paralleled the 3rd gain stage with a 50k plate and a 5k grid resistor.

That'a good stuff , thanks. When you say paralleled do you mean the 50k to the 100k plate load ? That would be the same as a single 75k plate resistor ?

Where did you institute your cut control ?

[funkmeblue]

instead of a 100k plate resistor I used a 50k plate resistor since I paralleled the two triodes in the 3rd gain stage and I used a 5k cathode resistor. Cut control is the same as the rocket and the comet 60

[passfan]

instead of a 100k plate resistor I used a 50k plate resistor since I paralleled the two triodes in the 3rd gain stage and I used a 5k cathode resistor. Cut control is the same as the rocket and the comet 60

Ahh... I see...found a use for the extra triode , thanks for the info. I realized the cut right after I hit the post button
Also, did you go all 6sl7 throughout the preamp or did you retain any of the 12's ?

[funkmeblue]

all 6sl7

[dave g]

An alternative to paralleling triodes would be to use the 4th triode as a cathode follower after the 3rd stage. If you do this, also drop the 3rd stage's 10k cathode resistor to 2.7 or 3.3k, and change the R7/C8 combo to something like 33k/.01uF or 68k/.005uF.

That's my special sauce.

[passfan]

Great stuff guys thanks a million.

[dartanion]

You may want to consider DC filaments. I did an Express style preamp with 6SL7s that sounds great. I crammed it all into a Pro Jr carcass, so I changed a few things to ensure stability since the chassis is so small.

[passfan]

I used Aiken's phase inverter http://www.aikenamps.com/ , I changed the 150k dropping resistor before the 3rd gain stage to 220k and added a cut control. The cut control allows me to crank the presence for more juicy gain, back off the cut to keeps the highs in check. I also paralleled the 3rd gain stage with a 50k plate and a 5k cathode resistor.

Was this neccessary or personal taste ?

[passfan]

You may want to consider DC filaments. I did an Express style preamp with 6SL7s that sounds great. I crammed it all into a Pro Jr carcass, so I changed a few things to ensure stability since the chassis is so small.

I have a larger chassis out of an older tube organ so plenty of room ti do whatever works best, thanks for the heads up.

[funkmeblue]

it was for personal taste. Just trying to make up for some of the loss in using 6sl7's

[dartanion]

Octal twin triodes can be noisy, hence the DC filaments. There is still plenty of gain even without another gain stage. You may also have to weed through a bunch of tubes to get non-microphonic, usable tubes.